This invention is generally directed to photoresponsive imaging members, and more specifically to layered photoconductive members. In one embodiment of the present invention, there are provided photoconductive layered imaging members comprised of a photogenerating layer with, for example, inorganic or organic photogenerating pigments, a charge or hole transport layer comprised of, for example, aryl amines as illustrated in U.S. Pat. No. 4,265,990 and U.S. Pat. No. 4,925,760, the disclosures of which are totally incorporated herein by reference, and wherein the hole transport molecules are dispersed in a resinous binder containing a liquid crystalline polymer. Further, in one embodiment of the present invention there is provided a photoresponsive imaging member or device comprised of a supporting substrate, a photogenerating layer, and a hole transport layer comprised of hole transport molecules dispersed in a resin binder comprised of various inactive resins such as polycarbonates and a liquid crystalline polymer, which polymer avoids, inhibits, or minimizes the undesirable crystallization of the charge transport molecules.
Some of the prior art photoconductive imaging members, especially the hole transport molecules, such as aryl amines, crystalline after extended imaging cycles, for example, after about 10,000 cycles to about 50,000 cycles, causing undesirable image quality, that is for example images with substantial background and/or poor resolution. Moreover, crystallization can cause cracking of the photoconductive layer, hence breakdown of the photorecptor and a shortened life span. It is believed that crystallization of the charge transport molecules is encountered, for example, after extended imaging cycles because of the slow diffusion of the charge transport molecule leading to crystallization within the polymer matrix of the charge transport layer. It is an object of this invention to provide a photoconductive member wherein there is incorporated into the above charge transport layer a thermotropic liquid crystalline resin or resins dispersed with the charge transport molecule and a resin binder thereby affording the aforementioned disadvantage. More specifically, with the aforementioned liquid crystalline resin there is avoided or minimized the diffusion of the charge transport molecule, hence crystallization of the charge transport molecule after extended imaging cycles of, for example, from about 50,000 to about 200,000 cycles is avoided or minimized. Furthermore, the minimization of the above mentioned crystallization avoids or minimizes the cracking of the photoreceptor belt, thereby increasing the lifetime expectancy of the photoconductive or photoreceptor layer to, for example, beyond 200,000 cycles in an embodiment of the present invention. Accordingly, the minimization or avoidance of crystallization of the charge transport molecules results in layered photoconductors of high sensitivity, low dark decay values, low residual potentials, and wherein these photoconductors possess high cyclic stability after an extention of imaging cycles, for example, from about 50,000 cycles to above 200,000 cycles in an embodiment of the present invention. The photoresponsive imaging members of the present invention can be selected for various electrophotographic imaging and printing processes, especially xerographic processes wherein, for example, latent images are formed thereon followed by development, transfer to a suitable substrate, and fixing by heat and/or heat and pressure.
Layered imaging members with hole transport layers are known, reference for example U.S. Pat. No. 4,265,990. These members are generally comprised of a supporting substrate, a photogenerating layer, and a charge transport layer wherein the charge or hole transport molecules thereof are dispersed in a resin binder, such as a polycarbonate. One problem associated with these members, especially when the hole transport molecules are comprised of certain aryl amines dispersed in a resin binder, is the undesirable crystallization thereof, which disadvantage is avoided or minimized with the imaging members of the present invention. Also, liquid crystalline polymers and their use as toner resins are known, reference U.S. Pat. No. 4,543,313, the disclosure of which is totally incorporated herein by reference. The liquid crystalline polymers of the aforementioned '313 patent can be selected as the thermotropic liquid crystalline resin for the imaging members of the present invention. Moreover, the thermotropic liquid crystalline polymers and preferably the random copolymers, and more preferably random copolyesters with three or more spacer groups therein as illustrated in copending application U.S. Pat. No. 4,891,293 entitled Toner and Developer Compositions with Thermotropic Liquid Crystalline Polymers, the disclosure of which is totally incorporated herein by reference, can be selected as the thermotropic liquid crystalline resin for the imaging member of the present invention. Examples of liquid crystalline thermotropic polymers are illustrated in FIGS. 1 to 16 attached hereto, which Figures correspond to or are substantially similar to those provided in the aforementioned copending application, wherein for FIGS. 1 and 2 X, Y and Z are independently selected from alkyl, alkylene, substituted alkyl, substituted alkylene, subject to the provision in a preferred embodiment that X, Y and Z represent different groups; m, n and o represent the number of monomer segments present in the copolymer. In FIGS. 3 to 16 m, n and o represent the number of monomer units, and R and R' independently represent hydrogen, hydroxyl, halogen, nitro, alkoxy, aryl alkoxy, alkyl and the like. Also, these may be selected as the thermotropic liquid crystalline resins for the imaging members of the present invention those crosslinked liquid crystalline resins as illustrated in copending application U.S. Pat. No. 4,973,539 entitled Toner and Developer Composition with Crosslinked Liquid Resins, the disclosure of this application being totally incorporated herein by reference. Examples of specific thermotropic liquid crystalline polymers illustrated in the aforementioned copending patent are described in FIGS. 17 and 18 submitted herewith, wherein X, Y and Z are, for example, independently selected from alkyl, alkylene, substituted alkyl and substituted alkylene subject to the provision that X, Y, and Z represent different groups; l, m, n and o represent the number of monomer segments present in the polymer; and p represents the percentage or amount of crosslinking segment with the provision that the numerical sum of l, m, n, o and p is equal to 100.
Illustrated in U.S. Pat. No. 4,315,981 are organic double layered electrophotographic recording materials comprised of an electroconductive support with a photoconductive double layer of organic materials, which consist of a homogeneous opaque charge carrier producing dyestuff layer obtained from an annealed quinone, or the substitution product thereof selected from the group consisting of dibenzopylene, quinone, anthraquinone, pyranthrone, dibenzathrone, and flaventhrone, and a transparent top layer of insulating materials of at least one charge transporting compound, which transport layer consists of a charge transporting monomer, reference for example column 2, lines 37 to 56. Further, as indicated in column 4, lines 1 to 22, as the formula 9 compound for the imaging member of the '981 patent there can be selected dibromo-8,16-pyranthrenedione (Indanthrene Orange RRTS, C.I. 59,705). Moreover, it is indicated in column 4, beginning at around line 53, that the organic dyestuff layer may be applied by vapor depositing the dyestuff in a vacuum. Also, this patent, the disclosure of which is totally incorporated herein by reference, discloses a number of resinous binders for the charge transport layer including polycarbonate resins, reference column 7. Further, in U.S. Pat. No. 3,871,882 there are disclosed layered electrophotographic recording materials containing an electroconductive support material and a photoconductive double layer of organic materials, reference for example the Abstract of the Disclosure. Other representative patents of background interest include 3,871,882 and 3,973,959.
In Konishiroku Kokai Japanese 59/184349/A2[84/184349], Oct. 19, 1984, there is disclosed the use of selected pyranthrones as charge generator layers in conjunction with hydrazone charge transport layers. Specifically, a solution coated dispersion of dibromo-8,16-pyranthrenedione in a polymer binder can be selected as the charge generator layer. Also, in U.S. Pat. No. 3,877,935 there are disclosed imaging members with dibromo-8,16-pyranthrenedione vacuum coated charge generator layers contiguous with poly(vinyl carbazole) charge transport layers.
Also of interest are U.S. Pat. Nos. 4,028,102; 4,399,207; 4,454,211; 4,554,231 and 4,714,666. In the '102 patent, there are illustrated diamine condensation products in double layered photoconductive recording elements with charge transports. More specifically, there is disclosed in the '102 patent condensation products of o-phenylamine diamine or 1,8-diaminylnaphthyline and 4,10-benzothioxanthrene-3,1'-dicarboxylic anhydride of the formulas as illustrated in column 2, and of the formulas 1 to 5, reference column 3, beginning at line 55. The '207 patent discloses electrophotographic photosensitive members with hydrozone compounds of the formula, for example, as illustrated in the Abstract of the Disclosure and in column 2. Examples of charge generating layer materials are illustrated beginning in column 16, line 65, and include, for example, phthalocyanine pigments, perylene pigments, and the like, typical examples of which are specifically recited in columns 17 through 26. The '211 patent discloses electrophotographic photosensitive members with pyrazoline charge transport materials, see for example column 2 , beginning at line 35. Specific organic photoconductive materials or change transporting materials for use in the invention of the '211 patent are illustrated according to the teachings thereof in columns 3and 4, formulas 1 and 2. Charge generating layers for the photoconductive members in the '211 patent are illustrated in column 42, beginning at line 11, and include, for example, organic substances such as perylium dyes, thioperylium dyes, perylene pigments, and the like with specific examples of charge generating materials being illustrated in columns 42 to 52. Also, it is disclosed in column 57 that a charge generating layer can be formed on aluminum plate by the vacuum deposition of a perylene pigment having carbon atom bridges at the 1, 12 and 6, 7 positions of the common perylene molecule. In U.S. Pat. No. 4,554,231, the disclosure of which is totally incorporated herein by reference there is illustrated an electrophotosensitive member comprised of a layer containing a hydrazone compound of the formula, for example, as illustrated in the Abstract of the Disclosure, which hydrazone compound is selected as charge transport material, reference column 5, line 30, and wherein there are selected various charge generations layer materials including, for example, perylium dyes, thioperylium dyes, perylene pigments and the like, see column 6, beginning at line 23, and note particularly columns 7 through 12. In U.S. Pat. No. 4,714,666, there are illustrated perylene tetracarboxylic acid imide pigments as electrophotographic recording materials, which pigments include those, for example, as represented by the formula 1, reference the Abstract of the Disclosure, and charge transport components.
Moreover, in U.S. Pat. No. 4,587,189, the disclosure of which is totally incorporated herein by reference, there are illustrated layered imaging members with photoconductive layers comprised of cis and transbis(benzimidazo)perylene pigments, and aryl amine hole transport layers wherein the amine can be dispersed in various resin binders such as polycarbonates.
Additionally, numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material such as vitreous selenium, or a composite layered device containing a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described, for example, in U.S. Pat. No. 3,121,006 wherein there are disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder.
There are also known photoreceptor materials comprised of inorganic or organic materials wherein the charge carrier generating, and charge carrier transport functions are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material. However, the art of electrophotography continues to advance and more stringent demands need to be met by the copying apparatus to, for example, increase performance standards, and to obtain quality images. Also, there have been disclosed other layered photoresponsive devices including those comprised of separate generating layers, and transport layers as described in U.S. Pat. No. 4,265,990 mentioned herein, the disclosure of which is totally incorporated herein by reference. Examples of photogenerating layers disclosed in this patent include trigonal selenium and phthalocyanines, while examples of transport layers include certain diamines as mentioned herein.
Many other patents are in existence describing photoresponsive devices including layered devices containing generating substances, such as U.S. Pat. No. 3,041,167 which discloses an overcoated imaging member containing a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in an electrophotographic copying system by, for example, initially charging the member with an electrostatic charge of a first polarity, and imagewise exposing to form an electrostatic latent image, which can be subsequently developed to form a visible image.
Furthermore, there are disclosed in U.S. Pat. No. 4,232,102 and 4,233,383 photoresponsive imaging members comprised of trigonal selenium doped with sodium carbonate, sodium selenite, and trigonal selenium doped with barium carbonate, and barium selenite, or mixtures thereof. Moreover, there are disclosed in U.S. Pat. No. 3,824,099 certain photosensitive hydroxy squaraine compositions. According to the disclosure of this patent, the squaraine compositions are photosensitive in normal electrostatographic imaging systems. The disclosures of each of the aforementioned patents are totally incorporated herein by reference.
In U.S. Pat. No. 4,508,803, the disclosure of which is totally incorporated herein by reference, there is described an improved photoresponsive device comprised of a supporting substrate, a hole blocking layer, an optional adhesive interface layer, an inorganic photogenerating layer, a photoconducting composition layer comprised of benzyl fluorinated squaraine compositions, and an aryl amine hole transport layer. Other representative patents disclosing photoconductive devices with squaraine components and hole transports therein include U.S. Pat. Nos. 4,507,408; 4,552,822; 4,559,286; 4,507,480; 4,524,220; 4,524,219; 4,524,218; 4,525,592; 4,559,286; 4,415,639; 4,471,041 and 4,486,520. The disclosures of each of the aforementioned patents are totally incorporated herein by reference.
Moreover, disclosed in the prior art are composite electrophotographic photosensitive materials with various azo compounds. For example, there is illustrated in Japanese Ricoh Patent Publication 6064354, published Apr. 12, 1985, composite photoconductors wherein one of the photoconductor layers contains an azo compound of the formulas as illustrated. Further, there are illustrated in several U.S. patents and publications layered organic electrophotographic photoconductor elements with azo, bisazo, or related compounds. Examples of these patents and publications include U.S. Pat. Nos. 4,400,455; 4,551,404; 4,390,608; 4,327,168; 4,299,896; 4,314,015; 4,486,522; 4,486,519 and 4,551,404; and Konishiroku Japanese Patent Laid Open Publication 60111247.
Other prior art that may be of background interest includes Japanese Patent 59-59686; Japanese Patent 59-154454; European Patent 100,581; U.S. Pat. No. 4,578,334; European Patent 40,402; U.S. Pat. No. 4,431,721; German Patent 3,110,954; R. O. Loutfy, Can. J. Chem 59, 544, (1981); and F. Graser and E. Hadicke, Liebigs Ann. Chem., 483 (1984).
Although photoconductive imaging members are known, there remains a need for improved imaging members. Additionally, there continues to be a need for layered photoresponsive imaging members comprised of, for example, arylamine hole transport components dispersed in a mixture of resins, one of which is a liquid crystalline polymer, such as those illustrated in the copending applications and patents mentioned herein, the disclosures of which have been totally incorporated herein by reference, which members will enable the generation of acceptable high quality images and wherein these members can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions, and wherein crystallization of the hole transport molecules is avoided or minimized. Moreover, there is a need for improved layered photoresponsive imaging members that are substantially inert to the users of such members. Additionally, there is a need for layered photoconductors wherein cracking of a layered photoreceptor belt with a hole transport layer is avoided or minimized, especially after an extended number of imaging cycles. Additionally, there is a need for layered photoconductors of high sensitivity, low dark decay values, low residual potentials, and which possess high cyclic stability. Furthermore, there continues to be a need for photoresponsive imaging members which can be positively or negatively charged thus permitting the development of images, including color images with positively or negatively charged toner compositions. Moreover, there is a need for the fabrication of a layered photoreceptor belt, including seamless belts, whereby the charge transport layer is comprised of from about 30 percent by weight of charge transport molecules to about 60 percent by weight, and more specifically from about 35 to about 50 percent by weight dispersed in a polymer matrix. Prior art fabrication of the photoreceptor belt by solution spray coating can suffer from defects associated with charge transport molecule crystallization, a problem solved or minimized with the present invention, and can preclude the use of more than 30 to 35 percent charge transport molecule in the preparation thereof. In one embodiment of the present invention, the selection of liquid thermotropic crystalline resins as a second resin in the hole transport layer comprised of hole transport molecules dispersed in a first resin such as a polycarbonate, reference U.S. Pat. No. 4,265,990, avoids or minimizes the undesirable crystallization of the charge transport molecules thereby allowing in an embodiment of the present invention the incorporation of up to, for example, 50 percent by weight of the charge transport molecule within the charge transport layer, and wherein defects associated with crystallization are avoided or minimized during solution fabricating spray coating processes. Similarly, there is a need for the fabrication of the charge transport layer by the dip coating process, whereby the charge transport molecule is employed in an amount of from about 30 to about 60 percent, and moreover from about 35 to 50 percent dispersed in a polymer matrix.
Prior art fabrication of photoreceptor drums by dip coating may also be undesirable because of defects associated with charge transport molecule crystallization and can preclude, for example, the use of more than 30 to 35 percent of such molecules. The use of the aforementioned liquid crystalline resins in the charge transport layer avoids or minimizes the crystallization of the charge transport molecule, thereby allowing up to 50 percent or more incorporation of the charge transport molecule without defects associated with crystallization during the dip coating process of fabricating the photoreceptor belt. Also, there is a need for disposable imaging members useful in xerographic imaging processes, and xerographic printing systems wherein, for example, light emitting diodes (LED), helium cadmium or helium-neon lasers, solid state AlGaAs diode lasers can be selected; and wherein these members are particularly sensitive to the visible and near infrared region of the spectrum, that is from about 400 to about 700 nanometers.